(1) Field of the Invention
The present invention relates generally to highly advantageous use of direct ultrasonic mixing of a sample in combination with, sample conveying and/or sample analysis.
(2) Description of the Prior Art
Prior art processes of preparation of solid samples for analysis (e.g. graphite furnace atomic absorption spectrometry (GFAAS) analysis) such as wet ashing (as for example described by Wolf, W. R. in "Human Nutrition Research, Beltsville Symposia in Agricultural Research", Allanheld, Osmun and Co., Totowa, N.J., 1981, Vol. 4, pp. 175-196) or dry ashing, have suffered from many drawbacks and disadvantages. Those prior art sample preparation techniques requiring digestion of the solid sample (such as "wet ashing", as for example by use of an oxident e.g. an oxidizing acid or peroxide) suffer from the disadvantages of: requiring a long period of time for digestion of the sample, possibility of losing the analyte through volatilization prior to analysis, loss of analyte due to its retention in insoluble residue, and the possibility of contaminating the sample. Direct analysis of solids by insertion directly into the graphite furnace suffers from the disadvantage of requiring very small sample sizes (sub milligram) which necessitate special weighing and sampling procedures, etc..
U.S. Pat. No. 4,528,159 (Jul. 9, 1985) to Liston discloses an automated analysis device, utilizing an ultrasonic horn (disposed in a water bath so that the water conducts the ultrasonic energy from the horn to the samples) utilized to break up and dissolve reagent tablets. Devices utilizing such an indirect mechanism for mixing may suffer from several drawbacks: (1) the ultrasonic energy from said horn may be dissipated by the water bath so that the samples are not adequately mixed; (2) such devices do not provide means for localizing the ultrasonic energy; (3) the ultrasonic energy may heat the water to an unacceptably high temperature and thereby necessitate cooling of the water bath to avoid overheating of the device. The Liston patent does not contemplate, direct ultrasonic mixing of samples, or using ultrasonics to mix a slurry or maintain a suspension of particles, or automated operation as utilized in the present invention.